Method and apparatus for the continuous casting of metal tubes



June 14, 1949. Ross; 2,473,221

METHOD AND APPARATUS FOR THE CONTINUOUS CASTING OF METAL TUBES Filed March 6, 1947 v W/ZINVEINTOR ATTORNEY Patented June 14, 1949 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR THE CON TINUOUS CASTING OF METAL TUBES Irving Rossi, West Orange, N. J.

Application March 6, 1947, Serial No. 732,734

6 'Claims.

not been successfully applied to the continuous casting of thin wall tubes. Much experimental and development work has been carried on to devise a satisfactory method, manyproposals have been made, and many patents have been issued which disclose methods and apparatus intended to solve the problem, but the fact remains that there isno method of casting thin wall tubes continuously in successful commercial operation at the present time, and such methods as have been used for making thick wall tubes have been slow and generally unsatisfactory.

One reason for the failure to solve the prob lem, in my opinion, is that all prior attempts have followed in a general way the basic concept utilized in the casting of solid ingot, namely, cooling the molten metal from the outside periphery, and although it is true that there have been many proposals to also cool the mandrel used to form the inner wall of the tube, the outside cooling has always predominated.

Such tubes as have been made by such methods have not been satisfactory. The surfaces, and particularly the inside surfaces have been rough and uneven, and,-due to the fact that-shrinkage occurs toward the outside wall, cracks frequently appear in the inside wall. The cry tal structure of the metal is frequently not uniform, and there has also been much diillculty from porosity.

It is an object of the present invention to overcome these difliculties and to provide a method and apparatus for continuously casting tubes of good quality, 1. e. with reasonably smooth sur-.

2 the inside of the tube, i. e. through a mandrel which forms the inside wall. In other words the cooling is entirely from the inside, rather than from the outside, or from both outside and inside as in prior methods. As a result, crystal growth proceeds outwardly from the inside wall rather than inwardly from the outside wall or in both directions as] in prior methods. Furthermore. while it will be seen from the foregoing that the mold wall which forms the outside wall of the tube is kept at a temperature such as to prevent any appreciable withdrawal of heat therethrough.

the said mold wall serves to limit the crystal growth from the inside and forms and smoothes the outer wall as the tube is withdrawn continuously therefrom.

Referring to the drawings, the apparatus comprises a mold block I of any suitable material such as graphite, said block having a cavity 2 in its upper portion serving as a reservoir in which a pool of molten metal may be maintained, such molten metal being supplied continuously from a suitable holding furnace (not shown) through a pipe or tube 3. The mold block may be supported in any suitable manner, as by a base plate 4, and may be held in place by. set screws 5, so that the block may be easily removed and replaced.

Extending downwardly through the bottom of ,the mold block i is a cylindrical mold passage 6 registering with a larger aperture 1 in the base plate so as to provide a through passageway for the continuous withdrawal of the formed tube. A

water cooled mandrel 8 projects downwardly into the mold'passage 6, said mandrel comprising an outer shell 9 having an inlet conduit Ill connected thereto,.and an inner tubular baiile II to cause circulation of the cooling water in the manner indicated by the arrows. An outlet conduit i2 is connected to the upper end of the tube ii. The bottom of the shell 9 is closed by a plate l3, but this plate is preferably provided with apertures ll which permit some of the cooling water to spray directly onto the interior wall of the solidifled tube T. Preferably the exterior wall of the shell 9 is tapered slightly to allow for shrinkage as the solidified metal becomes progressively cooler.

As previously stated, it is intended that all of the heat which is withdrawn from the molten metal to cause solidification thereof is withdrawn from the interior of the tube through the mandrel, and under most conditions, the heat from the pool of molten metal maintained in the cavity 2 keeps the mold block! at a temperature 3 sufficient to prevent any appreciable withdrawal of heat through the wall of the mold passage 8. However, the mold block may be provided with passages I5 to receive suitable heating elements by means of which the block may be maintained at any desired temperature.

The manner in which the tube is formed, i. e. by the outward growth of crystals from the water cooled mandrel, is shown in the drawings, in which, as crystal growth proceeds, the wall thickness of the tube increases gradually until the crystals forming at the outer wall of the tube engage the wall of the mold passage. It will be understood, of course, that the solidified tube is being withdrawn continuously from the mold and this movement causes the forming crystals along the outer wall of the tube to be smoothed as final solidification takes place. As final solidification takes place, slight shrinkage also takes place, so that the friction of the solidified metal against the wall of the mold passage is not serious.

If desired, a spray ring I6 may surround the tube below the point of emergence from the mold passage, and the cooling water applied to the outside of the tube, together with the cooling water applied to the inside through the apertures I4 carries oil the residual heat remaining in the tube after the solidification oi the molten metal which results entirely from the withdrawal of heat through the mandrel.

In the operation of the process, the solidified tube is withdrawn continuously, preferably by rollers (not shown), and if desired, the mandrel may be reciprocated in accordance with the teachings of Junghans Patent No. 2,135,133. That is, the mandrel 8 which provides the cooling surface and which therefore corresponds to the chilled mold of the Junghans patent, would be reciprocated, movin downwardly with the tube at the same rate at which the tube is being withdrawn, and moving upwardly at a more rapid rate.

It will be understood that the method and apparatus above described lend themselves easily to multiple continuous casting Where it may be desirable to cast a plurality of tubes simultaneously. Thus it is only necessary to increase the number of mold passages and the number of mandrels to permit multiple casting.

It will be understood that the inventions may be variously modified and embodied within the scope of the subjoined claims.

I claim as my invention:

1. A method for the continuous casting of metal tubes which comprises shaping the interior of the tube by means of a water cooled mandrel which constitutes the sole means for the withdrawal of heat to cause solidification of the molten metal, circulating cooling Water through all portions of said mandrel which are opposed to metal being solidified to cause crystal growth to proceed entirely outwardly from said mandrel, limiting the outward crystal rowth by means of a mold wall spaced from said mandrel, maintaining said mold wall at a temperature suflicient to prevent appreciable withdrawal of heat therethrough, and continuously withdrawing the solidified tube, the relative movement between the tube and the mold wall serving to smooth the outwardly growing crystals as final solidification takes place.

2. A method for the continuous casting of metal tubes which comprises shaping the interior of the tube by means of a water cooled mandrel which constitutes the sole means for the withmetal. circulating cooling water through all portions or said mandrel which are opposed to metal being solidified to cause crystal growth to proceed entirely outwardly from said mandrel, limiting the outward crystal growth by means of a mold wall spaced from said mandrel, maintaining said mold wall at a temperature sufiicient to prevent appreciable withdrawal of heat therethrough, continuously withdrawing the solidified tube, the relative movement between the tube and the mold wall serving to smooth the outwardly growing crystals as final solidification takes place, and reciprocating said mandrel in timed relation to the withdrawal of the solidified tube such that said mandrel moves downwardly with the tube at the same rate at which the tube is withdrawn, and moves upwardly at a more rapid rate.

3. A method for the continuous casting of metal tubes which comprises maintaining a pool of molten metal in a mold block having a mold passage extending therethrough, withdrawing heat to solidify molten metal entirely through a water cooled mandrel projecting into and extending throughout all portions of said mold passage wherein solidification takes place so that crystal growth proceeds entirely outwardly from said mandrel toward the wall of said mold passage and is limited thereby, maintaining said mold block at a temperature sufiicient to prevent appreciable withdrawal of heat through the wall of said mold passage and withdrawing the solidified tube continuously from said passage, the relative movement between the tube and wall of the mold passage serving to smooth the outwardly growing crystals as final solidification takes place.

4. A method for the continuous casting of metal tubes which comprises maintaining a pool of molten metal in a mold block having a mold passage extending therethrough, withdrawing heat to solidify molten metal entirely through a water cooled mandrel projecting into and ex tending throughout all portions of said mold passage wherein solidification takes place so that crystal growth proceeds entirely outwardly from said mandrel toward the wall of said mold passage and is limited thereby, maintaining said mold block at a temperature sufiicient to prevent appreciable withdrawal of heat through the wall of said mold passage withdrawing the solidified tube continuously from said passage, the relative movement between the tube and wall of the mold pasage serving to smooth the outwardly growing crystals as final solidification takes place, and reciprocating said mandrel in timed relation to the withdrawal of the solidified tube such that said mandrel moves downwardly with the tube at the same rate at which the tube is withdrawn, and moves upwardly at a more rapid rate.

5. In the art of casting metal tubes continuously in a mold comprising a water cooled mandrel and a surrounding mold wall providing an annular space therebetween, said water cooled mandrel extending from a point above said annular space to a point below the point of final solidification the method of casting which consists Of maintaining a pool of molten metal above said annular space, withdrawing heat throughout said water cooled mandrel to solidify molten metal entirely through said water cooled mandrel, so that crystal growth proceeds entirely outwardly from said mandrel toward the-surrounding mold wall-and is limited thereby, maintaining said mold wall at a temperature suflicient drawal of heat to cause solidification of the molten to prevent appreciable withdrawal of heat there- 5 through, and withdrawing the solidified tube continuously from said annular space, the relative movement between the tube and the mold wall serving to smooth the outwardly growing crystals as final solidification takes place.

6. Apparatus for the continuous casting of metal tubes, comprising a mold block, said block having a cavity therein in which a pool of molten metal is maintained and having a mold passage extending through said block from said cavity to the outside, a water cooled mandrel projecting into said mold passage and having a water cooled surface extending from a point above said passage to a point below the point of final soldification, said surface forming the sole means for the withdrawal of heat to cause solidification of the molten metal, and means for maintaining said mold block at a temperature sufficient to prevent appreciable withdrawal of heat from the molten metal. whereby crystal growth proceeds entirely outwardly from said mandrel toward the wall of said mold passage.

IRVING ROSSI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

